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aperature number vs f number

Started 10 months ago | Questions thread
Len Philpot
Len Philpot Contributing Member • Posts: 625
Re: aperature number vs f number

Lemming51 wrote:

Toronto Photography wrote:

F stops I get.

at f13 I have an apeture number of 7.3

Is it the same thing but a different scale or is it different.

What is the scale if the same thing? (like say Kelvin and Celsius?)

The "aperture number" of 7.3 is the number of stops smaller f/13 is compared to f/1.0

SquareRoot(2) ^ "aperture number" = f/# ("^" means raised to power or exponent)

Sqrt(2)^1 = f/1.4

Sqrt(2)^2 = f/2.0

...

Sqrt(2)^7.333 = f/13 (12.7)

Sqrt(2)^7.667 = f/14 (14.2)

Sqrt(2)^8 = f/16

That's the first time I've heard it expressed that way. To me it's far more convenient (and meaningful) to just think of it terms of stops (or half-stops, third-stops, etc. depending on your preference and camera settings). Makes doing the mental math easier, if and when required. YMMV.

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Len Philpot
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